"Article III, Section 3 is the only instance in which the U.S. Constitution defines a specific crime, that of treason. Treason is defined either as levying war against the United States or as giving "Aid and Comfort" to the enemies of the United States. The "Aid and Comfort" clause expands the definition of treason beyond physical acts of violence—e.g. to the passing of state secrets to another nation—but the Constitution also lays down specific legal procedures by which people accused of treason might be convicted of such an act. The Constitution further limits the punishment of treason to the person actually committing the act, not to family members or close associates. In 1807, in the treason trial of Aaron Burr, for his role in an alleged plan to lead parts of the Louisiana territory in a secessionist movement from the United States, Chief Justice John Marshall laid down further limitations on the definition of treason, establishing the doctrine of "constructive treason," meaning that the mere planning of an act that might be considered treasonous was not sufficient grounds for conviction; in order to be convicted of treason one actually had to commit, or at least be in the process of committing, the act. Moreover, the act of simply speaking, however stridently, in a manner that some might believe to be giving comfort to the enemy was given further protection under the free speech guarantees of the First Amendment."